New Zealand joined consensus supporting the adoption of this Convention in the United Nations General Assembly Third Committee in November 2006. At this time New Zealand also gave an explanation of position which is available on the Ministry of Foreign Affairs and Trade website.

That statement of position can be read here. The primary concerns seem to be around inconsistencies with existing international law, notably the Rome Statute of the International Criminal Court. However, the inconsistencies are not great (the
Rome statute defines "enforced disappearance" slightly differently, to include disappearances carried out by "political organisations" rather than just states, but also requires that they be "for a prolonged period of time"), and in both the examples given, they note that the Convention can be interpreted in a manner consistent with that statute and that New Zealand intends to do so. Furthermore, it is perfectly possible - and indeed, common practice - to sign a treaty with that sort of reservation on interpretation. However, the government does not intend to do so. According to an MFAT spokesperson, New Zealand "has no immediate plans" to sign or ratify the Convention.

Whether this is consistent with our claimed "strong support of human rights" is left as an exercise for the reader.